Tube of the magnetron type for ultra-short waves



Aug. 28, 1951 A. LERBS 2,566,087

TUBE OF THE MAGNETRON TYPE FOR ULTRA SHORT WAVES Filed April 24, 1948 '2Sheets-Sheet 1 INVENTOR ALFRED LE 5 By; "I I 5 AC NTS Aug. 28, 1951 A.LERBS TUBE OF THE MAGNETRON TYPE FOR ULTRA SHORT WAVES Filed April 24,1948 2 Sheets- Sheet 2 .z'hlvs/vral HLFRE. Lsnaa Patented Aug. 28, 1951TUBE OF THE MAGNETRON TYPE FOR ULTRA-SHORT WAVES Alfred Lerbs, Paris,France, assignor to Compagnie Generale de Telegraphic Sans Fil, acorporation of France Application April 24, 1948, Serial No. 23,063

In France June 13, 1947 3 Claims. (Cl. 315-39) This invention relates toelectronic tubes of the type generally disclosed by Dohler, Kleen andHuber in their application Serial No. 794,164 filed December 27, 1947,and now Patent No. 2,511,407, and which are intended for thetransmission of ultrav short waves and operating by an exchange ofenergy between an electro-magnetic wave cir culating in the interior ofthe tube and the electrons which are propelled by a circular movement,the invention being more particularly applicable to magnetrons and liketubes using a magnetic field which is at right angles to the electricfield accelerating the electrons.

The latter tubes have such a shape that the electro-magnetic wavecirculates therein with a decelerated speed and having more particularlya phase velocity equal to that of the electrons so that a multipleinteraction takes place between the wave and the electrons.

Hitherto magnetrons have been used exclusively for the generation ofoscillations and their easy self-starting has prevented them from beingused for other purposes and more particularly as amplifiers. Inmagnetrons with split anode the anode members may be considered aselementary self-inductances and capacities causing a certain retardationof the wave circulating therein, which wave is the result of theinteraction of the magnetic and electric fields created in the tube.

The electronic flux moves around a cathode having generally a circularsection. The selfexcitation of these tubes is more particularly due to.two phenomena; the wave traverses the same circular anode circuitseveral times; the same electron effect several complete revolutions andthus exchanges energy several times with the same field. These phenomenacan be compared to a retroactive coupling resulting in self-excitationof the tube which becomes unstable and is useless as regardsamplification.

The object of the invention is to provide a new mode of producingmagnetrons and like tubes in which this self-starting is avoided andwhich are consequently suitable for amplification and other associatedoperations, such as detection, etc. requiring stable operation.

According to the invention the tube is provided in addition to the usualoutput circuit with coupling means which enables incident oscillationswhich are to be amplified, detected, etc. to be applied thereto, thesetwo circuits being clearly separated from one another and the tube beingdimensioned in such a manner that the wave circulating therein, fed bythe incoming signal is so decelerated that its speed of propagationbecomes equal to that of the circulation or the electrons. In this waythe exchange of energy between them is greatly increased and one obtainsan increased output and good efliciency. On the other hand the tubereferred to is very easily self-started and in order to avoid this meansare provided such that the electrons after they have exchanged theenergy with the circulating wave during a single complete cycle nolonger return to the input circuit.

According to a modification use is made of a screen of conductingmaterial arranged between the input and output circuit.

According to another modification the effect of the screen is obtainedby a repulsive electric field. The decoupling of the input and outputcircuits is accentuated by the interruption of the trajectory ofpropagation of the electro-magnetic wave.

The invention is more particularly described with reference to theaccompanying drawings illustrating it by way of example only withoutlimiting it thereto, and wherein:

Figure l is a view largely diagrammatic illustrating a magnetron theanode A of which comprises a number of gaps terminating in cavityresonators C1, C2, C: etc.

Figure 2 is a similar view showing a modification of the coupling withthe outer circuit;

Figure 3 is a transverse sectional view of a com-, plete magnetronembodied in accordance with the invention;

Figure 4 is a sectional view along line bb' of Figure 3;

Figure 5 is a further sectional view along line cut of Figure 3; and

Figure 6 is a view similar to Figure 1 showin how feed-back is preventedby a repulsive field.

As shown in Figure l, the cavity resonators are uniformly distributedover the larger part of the periphery of the anode; the part between A1and A2 is not recessed. The incident oscillations are introduced by anysuitable means such as the loop E in one of the cavities, namely C1. Theenergy is taken off by the loop S inserted in another cavity. Themagnetic field is applied in a direction B, determined by the mutualposition of the inlet and outlet terminals and a continuous potential isapplied between the cathode K and the anode imparting to the latter apositive potential and creating the radial field of the acceleration ofthe electrons. Under the action of these two fields the electrons aredisplaced along .a trajectory shown by the circular arrow F. The signalapplied at E produces an electromagnetic tion and by suitablydimensioning the tube the speed can be made substantially equal to thatof the electrons. The speed of the electrons is tion:

V=E1/B E1 being the radial electric field and B the ma'gnetic field.

On the other hand one could consider the circular space between theanode and the cathode as a succession of coupled circuits such as theone shown in dotted lines to which one could apply the theory oftransmission lines; in these circumstances the phase velocity Vp of thewave circulating therein would be:

In this formula Z is the linear extension of "an elementary quadripoleof this line along the periphery of the anode, L is the seriesselfinductance and C the transverse capacity of the elementaryquadripole such as illustrated in dotted lines. For determining thesevalues the couplings between the elementary circuits have also to beborne in mind. In order to increase the power of the tube and itsefiiciency one should ensure that augmented interaction takes placebetween the electrons and the wave and for this purpose make V and V1)equal to one another.

A tube as above described has the very pronounced tendency to start onits own initiation and'for this reason would not'be suitable'foramplification.

The self-starting is prevented by suppressing feed-back between theinput and output circuits and more particularly by stopping theelectrons and also the wave after they have traversed a complete cycle.For this purpose a break of the transmission is provided in the regionbetween the dotted lines M1 and M. In this figure the break is ensuredby means of a screen of conducting material P'P to which a suitablepotential is preferably applied with respect to the cathode and moreparticularly a positive potential with respect thereto by connecting itfor example to the body of the anode. On the other hand the circuit ofthe wave is interrupted by dispensing with "the cavity resonatorsbetween A1 and A modification is shown in Figure 2 in which the couplingwith the outer circuits is more suitable for adaptation to theconditions of these circuits, being more particularly suitable forconnection to an aerial.

The incoming and outgoing waves are sent through rectangular guides GEand Gs connected to the resonant cavities -by guiding sections of thewave length M4 intended for the transformation of the voltage.

Referring to Figures 3, '4 and 5, a metallic envelope T contains acathode K, ananodeA, and :ascreen :P, these electrodes being-providedOwing 1 given by the equa- I in serpentine.

with input and output passages E, O, P, K. The magnetic poles N and S,seen in Figure 5, furnish the magnetic field. In order to increase theinteraction efiiciency between the retarded wave and the electrons, itis of interest to increase the number of anodic slots 0. Such anarrangement is equivalent to the increase of the number of coupledcircuits and thus there is assured a wider pass-band. The section ofFigure 4 shows a fragmentary View of the anode and shows that the anodicelements are arranged The arrows F-F indicate the sense of rotation ofthe electrons, and the arrow 13 indicates the direction of magneticfield.

Finally in the arrangement according to Figure 6 the feed-back isprevented by the creation of a repulsive field between the inlet andoutlet circuits by means of an auxiliary electrode U to which a suitablepotential is applied relatively to the cathode.

Although the tubes hereinbefore described show certain similarities withthemagnetroh they differ therefrom in various important respect's. Theyare provided with an outlet electr'ode and withan inlet electrodebetweenwhich means are provided which prevent the retroaction. They areso dimensioned that the incoming signal produces an electro-magneticwave which is displaced at the same speed as the electrons; the magneticfield directed towards the cathode has to-be constant and have at thesame time a definite polarity, whereas in the case of magnetrons itsinversion does not infiu'ence their operation. Finally the arrangementof their electrodes cannot be circular and in certain cases the cathodecan even be out of axial alignment with respect to the anode.

I claim:

1. Ultra high frequency amplifier tube com--; prising, a cylindricalcathode, a cylindrical anode surrounding said cathode and provided withan input terminal and an output terminal for ultra high frequency, adelay line extending in the plane perpendicular to the cathode axis andincorporated in said anode on an are comprised between the inputterminal and the output terminal, means for connecting a voltage sourcebetween the cathode and anode for producing an electric field betweenthese two electrodes, means for producing a magnetic field parallel tothe axis of the cathode and in such direction that the electrons emittedby the cathode are displaced, under, the combined influence of theelectric field and of the magnetic field, parallel to the delay line inthe direction from the input to the output terminals, and meanscomprising a screen with means whereby a voltage negative respecting thecathode may be impressed thereon and arranged between the cathode andthe anode within the limits of the arc complementary to that occupied bythe delay line, for preventing the electrons and the ultra high'frequency of the output from following the path between the outputterminal and the input terminal alon said complementary arc.

2. Ultra high frequency amplifier tube comprising, a cylindricalcathode, a cylindrical anode surrounding said cathode and provided withan input terminal and an output terminal for ultra high frequency, adelay line extending in the.

plane perpendicular to the cathode axis and incorporated in said anodeon an are comprised between the input terminal and the output terminal,means for connecting a voltage source between :the cathoderand anodeiorproducing an electric field between these two electrodes, means forproducing a magnetic field parallel to the axis of the cathode and insuch direction that the electrons emitted by the cathode are displaced,under the combined influence of the electric field and of the magneticfield, parallel to the delay line in the direction from the input to theoutput terminals, and means comprising an electrode with means whereby avoltage negative respecting the cathode may be impressed thereon andarranged outside the electronic path in the anodic zone complementary tothe are occupied by the delay line, for preventing the electrons and theultra high frequency of the output from following the path between theoutput terminal and the input terminal along said complementary are.

3. Ultra high frequency amplifying tube comprising, a cylindricalcathode, a cylindrical anode surrounding said cathode and provided withan 20 these two electrodes, means for producing a magnetic fieldparallel to the axis of the cathode and having a direction such that theelectrons emitted by the cathode are displaced, under the combinedinfluence of the electric field and of the magnetic field, parallel tothe delay line in the direction of the input to the output terminal, andmeans outside the electron path in the anodic zone complementary to thearc occupied by the delay line for preventing the electrons and theultra high frequency from the output from following the path between theoutput terminal and the input terminal along the complement of theaforesaid arc.

ALFRED LERBS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,419,172 Smith Apr. 15, 19472,423,716 McArthur July 8, 1947 2,429,291 Okress Oct. 21, 1947 2,433,481Retherford Dec. 30, 1947 2,439,401 Smith Apr. 13, 1948

